We recently had a structural failure occur in our Living-Dining Room. The ceiling fell . The problem as far as we can tell was purely structural. No water or other obvious problems. The nails looked like they just pulled free from the studs over time. We could not see any dicerning issue in the ceiling only heard the ceiling creaking/popping that evening until it fell. As though the weight of the Rocklath, plaster, drywall was too much, if a few nails came free the structure was no longer being supported by the nails. Our house was built in the early 1930's not of 2x4's but of steal studs & I-Beams. See attached photos. The ceiling is constructed just as our walls are, drywall, rocklath then a skimcoat of plaster then paint ontop. ? - Should we insulate the ceilings before we put new drywall up? Above the living room is a finished upstairs bedroom/closet. Above the Diningroom is a rubberized Flat roof. I think we should at least insulate the Diningroom ceiling if nothing else.